1. Field of the Invention
The present invention relates to a high frequency filter and, more particularly, to an arrangement of dielectric filter of MIC (microwave integrated circuit) type.
2. Description of the Prior Art
Generally, the dielectric filter of this type has a base plate made of electrically non-conductive material and having a ground electrode, input electrode, output electrode and capacitance electrodes aligned between the input and output electrodes with a predetermined spacing. A plurality of dielectric resonators are mounted on the base plate, each having an outer conductor which is connected to the ground electrode and an inner conductor which is connected to a particular capacitance electrode.
The prior art dielectric filters of the above described type further has a casing mounted on the base plate so as to electrically shield the dielectric resonators. The external connection to the filter is done by terminal pins which are connected to input and output electrodes and ground electrode, respectively. Therefore, the prior art filter is presented in a unit element. Such a prior art dielectric filter is disclosed, for example, in U.S. Pat. No. 4,431,977 to Sokola et al, U.S. Pat. No. 3,121,847 to Pakan and U.S. Pat. Nos. 4,223,287, 4,245,198, 4,276,525, 4,342972, 4,151,494, and 4,546,334 all to Nishikawa et al.
When in use, the prior art dielectric filter is mounted on a substrate on which a microwave integrated circuit (MIC) is formed. The electric connection of the filter unit to the strip line of the MIC is done, for example, by socketing the terminal pins on the filter unit to the sockets formed on the substrate of the MIC. The sockets may be formed on the filter unit and the terminal pins may be formed on the substrate. In any event, it is necessary to form the sockets and terminal pins, which results in the increase of the manufacturing cost. Furthermore, to ensure the connection between the socket and pin, a solder beads may be applied at the connection. This results in the extra manufacturing step. Also, because the connection is done by the socket and pin, it is difficult to make an appropriate impedance matching between the filter unit and the MIC.